SAN FRANCISCO (AP) — D’Angelo has added the Outside Lands music festival to his list of cancellations due to an unspecified medical emergency.

The soul singer had been forced to cancel U.S. dates last week due to illness and also will miss shows in Chicago and San Diego this week. Chic, featuring Nile Rodgers, will step into D’Angelo’s slot Friday night at Outside Lands where he was supposed to close the Sutro Stage.

The nature of D’Angelo’s illness was unclear. A publicist didn’t immediately respond to an email inquiry. The singer, whose real name is Michael Archer, has been slowly returning to public performances over the last year after more than a decade away from the spotlight and is expected to soon release his first album since 2000.